Catalogue - Application Guide catalog - Watlow - (Version JPG)

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Thermocouple cable, Sensor, Thermocouple wire, Radiant heater, Coil heater

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Application Guide

Ref. 9

Electric Heaters

Heat Loss Factors and Graphs

Heat Losses at 70°F Ambient

How to use the graph for more accurate calculations

Ref. 9—Convection curve correction factors:

■

Heat Losses from

ate

aces

—

Convection—Vertical Surface Combined Radiation and Con

vection—

—

Combined Radiation and Convection— Oxidized Steel-----------

7 '

_ >

/ , /

•

2000

1800

1600

For losses from top surfaces or from horizontal pipes

Multiply convection curve value by 1.29

1400


	For side surfaces	Use convection
	and vertical	curve directly
	pipes
	For bottom	Multiply
	surfaces	convection curve
		value by 0.63

Ï o u ra

1200

O 1000

¡5 Q.

E a>

Radiation Curve Correction Factors

The radiation curve shows losses from a perfect blackbody and are not dependent upon position. Commonly used block materials lose less heat by radiation than a blackbody, so correction factors are applied. These corrections are the emissivity (e) values listed to the right:

Total Heat Losses =

Radiation losses (curve value times e) + Convection losses (top) + Convection losses (sides) + Convection losses (bottom) = Conduction losses (where applicable)

800

600

400

200

0.1 0.2 0.3 0.4 0.6 0.8 1 2 3 4 5 6 7 8 910 20 30 40 5060 80100

Losses—W/in²

Application Guide catalog - Watlow - #26

Thermocouple cable, Sensor, Thermocouple wire, Radiant heater, Coil heater